Apparatus comprising a mechanical arm that can hold and guide a payload have been shown to be of valuable assistance in various industrial procedures or medical procedures, for example, manipulation of tools, manipulation of cameras or sensors, etc.
These apparatus typically have one or more degrees of freedom and may be manually driven in that the one or more degrees of freedom may be equipped with a brake with motive force being provided by a human user, or may be automated in that at least one degree of freedom is driven by a computer controlled actuator.
A balancing mechanism may be used to counteract the force of gravity for hinged and/or articulated arm. Elimination or reduction of the effects of gravity allow the use of smaller power sources, gears and/or less effort exerted by a manual user. This is desirable from a cost standpoint and allows for a more compact design which, in turn, allows greater accessibility to the workspace.
Several counterbalancing mechanisms have been previously disclosed, for example, U.S. Pat. No. 4,756,204, U.S. Pat. No. 4,546,233, or U.S. Pat. No. 4,500,251.
Balancing mechanisms used on articulated arms and hinge mechanisms include counterweights. However, the use of counterweights can result in added mass and increase in arm inertia.
A tension spring or passive pneumatic balancer may be used for balancing within a small angle or within a single quadrant (i.e. from a horizontal to vertically upward orientation). However, conventional tension springs typically do not adequately balance the gravitational load. Also, it is inherent in most spring balancing methods that complete balance is possible only for one or two configurations of the arm and spring combination. As the robot arm moves away from that configuration in either of two possible directions, an unbalance is generated. Thus, a danger of this mechanism may be drifting or falling under the force of gravity when actuation is removed or reduced. Therefore, such mechanisms are usually provided with brakes to alleviate the potential danger, or are overbalanced against gravity.
Compression springs operating on small moment arms may overcome an angular limitation problem and offer better balance over the entire range of travel of the robot's arm. However, the problem of drift or falling under gravity also exists with compression springs.
It is an object of an aspect of the present invention to provide a counterbalance assembly for a joint of a mechanical arm.